1. Field of the Invention
This invention relates to personal computers, and more particularly to a front panel display for a personal computer.
2. Description of the Related Art
Personal computers (PC's) have become immensely popular. These PC's were originally manufactured by International Business Machines Corp. (IBM) of Armonk, N.Y., but are now made by many vendors. These PC's typically have a keyboard, monitor, and a main chassis or "box" that houses the central processing unit (CPU), which is mounted on a main or motherboard. This main chassis is also referred to as the system unit.
While most information is displayed to the user on the monitor, most PC's also have a small display on the front of the system unit. This small front-panel display consists of a few light-emitting diodes (LEDs). Small LEDs indicate if the power is on, if the hard disk is being accessed, and if "turbo mode" is active. While these small LEDs can only indicate on or off, a few digits of numerical information can also be displayed by 7-segment LED matrixes. Many PC's have two such digits, allowing for display of the speed of the PC, in MegaHertz (MHz). For example, a 33 MHz PC may have a front-panel display showing "33", while a 90 MHz PC would display "90".
More recent PC's have a "turbo" button on the front panel. This button activates "turbo mode". Turbo mode is misnamed because it slows down the PC. It is sometimes called "de-turbo mode" to more accurately describe its function. Turbo mode is needed to slow fast PC's down so that older software that uses timing loops may appear to run at the proper speed. Older DOS games in particular were written to display an image on the monitor for a certain period of time that was set by executing a program loop a certain number of times. While this worked for older 8 MHz PC's, a newer 90 MHz PC would display the game's image for only 1/10-th of the time that the 8 MHz PC would.
The front panel display may change to reflect the slower speed of de-turbo mode. For example, a 90 MHz PC would display "90" when operating at full speed, but "08" or "8" when operating in de-turbo mode. This gives the user an indication of the speed of the PC.
The speed of the PC may be slowed down by switching the clock to the CPU. Other ways to slow the PC down include adding wait states to certain accesses, or periodically asserting HOLD to the CPU to periodically pause operation of the program. De-turbo mode may be entered on some PC's by a hotkey combination of keyboard keys, such as CTL-ALT-+.
While the front panel display provides a convenient way to display information to the user, it remains one of the most under-utilized parts of a PC. Prior-art front panels on PC's typically can only display two numbers--the speed in MHz of the PC when at full speed and when in de-turbo mode. Jumpers are often used to select the numbers to display when in de-turbo or standard modes. However, the front panel has been restricted to displaying the speed of the PC.
What is desired is a front-panel display on a PC that displays other information to the user besides the speed of the PC. It is further desired to provide a communication link from the PC's motherboard to the front-panel display so that information from a program executing on the CPU may be sent to the front panel for display, under control of the PC's software or firmware.